This invention relates to imaging materials. In a preferred form it relates to base materials for photographic papers.
In the formation of photographic paper it is known that the base paper has applied thereto a layer of polyolefin resin, typically polyethylene. This layer serves to provide waterproofing to the paper and provides a smooth surface on which the photosensitive layers are formed. The formation of the smooth surface is controlled by both the roughness of the chill roll where the polyolefin resin is cast, the amount of resin applied to the base paper surface, and the roughness of the base paper. Since the addition of polyolefin resin to improve the surface adds significant cost to the product it would be desirable if a smoother base paper could be made to improve the gloss of photographic paper. Sheet properties such as smoothness may be improved through the addition of inorganic particulate filler materials to paper making furnishes.
It has been proposed in U.S. Pat. No. 5,866,282 (Bourdelais et al.) to utilize a composite support material with laminated biaxially oriented polyolefin sheets as a photographic imaging material. In U.S. Pat. No. 5,866,282 biaxially oriented polyolefin sheets are extrusion laminated to cellulose paper to create a support for silver halide imaging layers. The biaxially oriented sheets described in U.S. Pat. No. 5,866,282 have a microvoided layer in combination with coextruded layers that contain white pigments such as TiO2 above and below the microvoided layer. The composite imaging support structure described in U.S. Pat. No. 5,866,282 has been found to be more durable, sharper and brighter than prior art photographic paper imaging supports that use cast melt extruded polyethylene layers coated on cellulose paper.
The addition of inorganic particulate fillers such as clay, TiO2, calcium carbonate and talc, improves sheet properties because the particles fill in the void spaces within the fiber mat resulting in a denser, brighter, smoother, and more opaque sheet. In some instances, paper can also be made cheaper because the filler used is less expensive than cellulose fiber.
The substitution of fiber with filler in the sheet is, however, limited by the resultant reduction in strength, density, and sizing properties. As the proportion of filler is increased, fiber-to-fiber bonding is disrupted resulting in a reduction in sheet strength and stiffness properties. Due to the filling of sheet voids with increasing filler addition, sheet density is increased. The increased hydrophilicity of inorganic fillers over chemically-treated (sized) paper-making fibers also results in a reduction in sizing properties of the paper. All of the above undesirable changes limit the use of filler materials in various applications, particularly in photographic paper, where even a small change in any of the above properties can seriously affect effectiveness of the resulting image as a photograph. In addition to the above, the choice of filler is also limited because of it""s impact on sheet properties or because of its undesired presence in processing steps. For example, the filler material should not be photographically active or degrade the performance of the photographic element in which it is utilized.
The use of calcium carbonate as a filler in photographic base, though desirable in many ways, is problematic because of the tendency for calcium carbonate to leach out into developer solutions and subsequently precipitate in the form of calcium salts. Improved calcium carbonate retention is desirable to achieve a smoother and higher opacity photographic paper.
It is an object of the invention to provide an imaging material that has improved surface properties.
Another object of this invention is to provide an imaging material that is more opaque.
These and other objects of the invention are accomplished by a paper comprising between 2 and 8% calcium carbonate in a paper having a surface roughness average of between 0.10 and 0.44 xcexcm, a fiber length of the individual fibers of said paper of between 0.4 and 0.6 mm, and a density of between 1.05 and 1.20 grams/cc. By proper mechanical development of the fibers and densification of the sheet, a fiber matrix is formed which makes it more difficult for the calcium carbonate to exit the fiber mass. This improved retention of calcium carbonate makes leaching of calcium carbonate in photofinishing less likely. It also leads to a reduction in dust levels during slitting. Better retention of the calcium carbonate makes its usage a feasible alternative to more conventional fillers such as titanium dioxide.
The invention provides an improved paper for imaging elements. It particularly provides an improved paper for imaging elements that are smoother, are more opaque, and are low cost.
The invention has numerous advantages over prior practices in the art. The invention provides an imaging element that has a smoother surface, increasing the commercial value of the imaging element. By improving the smoothness of the paper, the contrast range of the paper in improved as the blacks appear blacker and the whites appear whiter. Further, the invention provides an imaging paper that is lower cost as the basis weight of the paper and the paper chemistry are reduced compared to traditional photographic paper bases. Another advantage is the improved knife-wear as this base paper is cut in both the cross and machine directions in imaging converting applications such as the slitting of wide rolls of imaging support, punching of imaging elements as in photographic processing equipment and chopping as in photographic finishing equipment. A further advantage is the reduction in imaging element curl over a wide range of relative humidity when compared to standard imaging element products. By improving the opacity of the paper, the amount of undesirable show through when images are viewed by consumers is reduced. These and other advantages will be apparent from the detailed description below.
The terms as used herein, xe2x80x9ctopxe2x80x9d, xe2x80x9cupperxe2x80x9d, xe2x80x9cemulsion sidexe2x80x9d, and xe2x80x9cfacexe2x80x9d mean the side or toward the side of a photographic member bearing the imaging layers. The terms xe2x80x9cbottomxe2x80x9d, xe2x80x9clower sidexe2x80x9d, and xe2x80x9cbackxe2x80x9d mean the side or toward the side of the photographic member opposite from the side bearing the photosensitive imaging layers or developed image. The term xe2x80x9cface sidexe2x80x9d means the side opposite the side of cellulose paper formed on a Fourdriner wire. The term xe2x80x9cwire sidexe2x80x9d means the side of cellulose paper formed adjacent to the Fourdriner wire.
For the cellulose paper of the invention, calcium carbonate is added to the paper fiber prior to the paper being formed on the Fourdriner wire. Calcium carbonate is preferred as it has been shown to lower cost as the basis weight of the paper and the paper chemistry are reduced compared to traditional high quality paper bases. Another advantage of the addition of the calcium carbonate is the improved knife-wear as the paper is cut in both the cross and machine directions. Examples include converting applications such as the slitting of wide rolls of imaging support, punching of imaging elements as in photographic processing equipment and chopping as in photographic finishing equipment.
A paper comprising between 2 and 8% calcium carbonate in a paper having a surface roughness average of between 0.13 and 0.44 xcexcm, a fiber length of the individual fibers of said paper of between 0.4 and 0.58 mm, and a density of between 1.05 and 1.20 grams/cc is preferred. This paper is preferred because it is smooth, strong and opaque providing a high quality cellulose paper for use in as a reflective imaging output media where smoothness, tear resistance and opacity are perceptually preferred by consumers. The calcium carbonate addition between 2 and 8% provides opacity to the high quality, smooth cellulose paper of the invention. Calcium carbonate addition less than 1% does not sufficiently improve the opacity of the paper. Calcium carbonate addition above, 10% is difficult to manufacture. The most preferred amount of calcium carbonate added to the cellulose paper is between 3 and 5 weight percent. Between 3 and 5% cost, manufacturing efficiency and opacity have been found to be optimum.
Calcium carbonate as a filler presents many advantages. It is not photographically active. It is compatible with the use of optical brightening agents. It can be manufactured to exacting specifications in size, shape, and purity. It is of low cost. However, calcium carbonate decomposes at acidic pH""s limiting its use severely. For example, the use of calcium carbonate as a filler is typically limited to alkaline paper-making operations since calcium carbonate is known to decompose to calcium hydroxide and carbon dioxide when exposed to the acidic pH of acid paper-making operations. In photographic paper, in particular, the paper is exposed to developer solutions that typically are of pH 3.0. Any calcium carbonate present in the paper that is exposed to the developer solution is decomposed causing calcium ions to exit the paper and enter the developer solution bath. Over time, the calcium ion concentration within the developer builds until calcium precipitates in the form of a salt, forming stalagmites within the developer solution batch. These stalagmites rub against the moving paper web causing scratches that render the resulting prints unusable. The use of calcium carbonate in photographic paper, otherwise desirable because of the improved smoothness and opacity imparted to the sheet, is thus prohibited.
The calcium carbonate used may be either precipitated or ground. Examples of CaCO3 that are acceptable for addition to the cellulose paper of this invention include the family of precipitated calcium carbonates sold under the tradenames Albacar, Albalfil, and Albagloss by Specialty Minerals, Inc. and the family of ground calcium carbonates sold under the tradenames Omyafil and Omyapaque by Omya, Inc and, in particular, Albacar HO made by Specialty Minerals, Inc., Omyafil made by Omya, Inc.
The smooth, strong paper of the invention may also contain TiO2. TiO2 has been shown to improve the opacity of the paper and provide a high quality white appearance. TiO2 and calcium carbonate may also be used in combination. The preferred ratio of calcium carbonate addition to TiO2 addition is between 2:1 and 6:1. Below a 2:1 ratio, the manufacturing and cost advantages of calcium carbonate are reduced. Above a 7:1 ratio, little improvement in paper whiteness or opacity is observed to justify the additional expense of the TiO2. The most preferred ratio of calcium carbonate addition to TiO2 addition is 4:1. At a 4:1 ratio, the opacity, cost and whiteness have been found to be optimized for silver halide imaging systems.
The TiO2 used may be either anatase or rutile type. Examples of TiO2 that are acceptable for addition of cellulose paper are DuPont Chemical Co. R101 rutile TiO2 and DuPont Chemical Co. R104 rutile TiO2. Other pigments to improve photographic responses may also be used in this invention, pigments such as talc, kaolin, CaCO3, BaSO4, ZnO, TiO2, ZnS, and MgCO3 are useful and may be used alone or in combination with TiO2.
In the case of silver halide photographic systems, suitable cellulose papers must not interact with the light sensitive emulsion layer. A photographic grade paper used in this invention must be xe2x80x9csmoothxe2x80x9d as to not interfere with the viewing of images. The surface roughness of cellulose paper or Ra is a measure of relatively finely spaced surface irregularities on the paper. The surface roughness measurement is a measure of the maximum allowable roughness height expressed in units of micrometers and by use of the symbol Ra. For the paper of this invention, long wave length surface roughness or orange peel is of interest. For the irregular surface profile of the paper of this invention, a 0.95 cm diameter probe is used to measure the surface roughness of the paper and thus bridges all fine roughness detail. The preferred surface roughness of the paper is between 0.13 and 0.44 micrometers. At surface roughness greater than 0.44 micrometers, little improvement in image quality is observed when compared to current photographic papers. A cellulose paper surface roughness less than 0.13 micrometers is difficult to manufacture and costly.
The preferred basis weight of the cellulose paper of the invention is between 117.0 and 195.0 g/m2. A basis weight less than 117.0 g/m2 yields a imaging support that does not have the required stiffness for transport through photofinishing equipment and digital printing hardware. Additionally, a basis weight less than 117.0 g/m2 yields a imaging support that does not have the required stiffness for consumer acceptance. At basis weights greater than 195.0 g/m2, the imaging support stiffness, while acceptable to consumers, exceeds the stiffness requirement for efficient photofinishing. Problems such as the inability to be chopped and incomplete punches are common with a cellulose paper that exceeds 195.0 g/m2 in basis weight. The preferred fiber length of the paper of this invention is between 0.40 and 0.60 mm. Fiber Lengths are measured using a FS-200 Fiber Length Analyzer (Kajaani Automation Inc.). Fiber lengths less than 0.35 mm are difficult to achieve in manufacturing and as a result expensive. Because shorter fiber lengths generally result in an increase in paper modulus, paper fiber lengths less than 0.35 mm will result in a photographic paper this is very difficult to punch in photofinishing equipment. Paper fiber lengths greater than 0.62 mm do not show an improvement in surface smoothness.
The preferred density of the cellulose paper of this invention is between 1.05 and 1.20 g/cc. A sheet density less than 1.05 g/cc would not provide the smooth surface preferred by consumers. A sheet density that is greater than 1.20 g/cc would be difficult to manufacture requiring expensive calendering and a loss in machine efficiency.
The machine direction to cross direction modulus is critical to the quality of the imaging support as the modulus ratio is a controlling factor in imaging element curl and a balanced stiffness in both the machine and cross directions. The preferred machine direction to cross direction modulus ratio is between 1.4 and 1.9. A modulus ratio of less than 1.4 is difficult to manufacture since the cellulose fibers tend to align primarily with the stock flow exiting the paper machine head box. This flow is in the machine direction and is only counteracted slightly by fourdrinier parameters. A modulus ratio greater than 1.9 does not provide the desired curl and stiffness improvements to the laminated imaging support.
A cellulose paper substantially free of dry strength resin and wet strength resin is preferred because the elimination of dry and wet strength resins reduces the cost of the cellulose paper and improves manufacturing efficiency. Dry strength and wet strength resins are commonly added to cellulose photographic paper to provide strength in the dry state and strength in the wet state as the paper is developed in wet processing chemistry during the photofinishing of consumer images. In this invention, dry and wet strength resin are no longer needed as the strength of the paper is significantly improved when laminated with high strength biaxially oriented polymer sheets to the top and bottom of the cellulose paper.
Any pulps known in the art to provide image quality paper may be used in this invention. Bleached hardwood chemical kraft pulp is preferred as it provides brightness, a good starting surface and good formation while maintaining strength. In general, hardwood fibers are much shorter than softwood by approximately a 1:3 ratio. Pulp with a brightness less than 90% Brightness at 457 nm is preferred. Pulps with brightness of 90% or greater are commonly used in imaging supports because consumers typically prefer a white paper appearance. A cellulose paper less than 90% Brightness at 457 nm is preferred as the whiteness of the imaging support can be improved by laminating a microvoided biaxially oriented sheet to the cellulose paper of this invention. The reduction in brightness of the pulp allows for a reduction in the amount of bleaching required thus lowering the cost of the pulp and reducing the bleaching load on the environment. Additionally, the use of calcium carbonate as a filler instead of TiO2 permits the more efficient use of optical brightening agents since TiO2 competes with optical brighteners for uv radiation incident upon the imaging element, preventing optical brighteners from contributing filly to the brightness of the imaging element. Calcium carbonate is advantaged since it does not exhibit this property.
The cellulose paper of this invention can be made on a standard continuous Fourdrinier wire machine. For the formation of cellulose paper of this invention, it is necessary to refine the paper fibers to a high degree to obtain good formation. This is accomplished in this invention by providing wood fibers suspended in water bringing said fibers into contact with a series of disc refining mixers and conical refining mixers such that fiber development in disc refining is carried out at a total specific net refining power of 44 to 66 KW hrs/metric ton and cutting in the conical mixers is carried out at a total specific net refining power of between 55 and 88 KW hrs/metric ton, applying said fibers in water to a forming member to remove water, drying said paper between press and felt, drying said paper between cans, applying a size to said paper, drying said paper between steam heated dryer cans, applying steam to said paper, and passing said paper through calender rolls. The preferred specific net refining power (SNRP) of cutting is between 66 and 77 KW hrs/metric ton. A SNRP of less than 66 KW hrs/metric ton will provide an inadequate fiber length reduction resulting in a less smooth surface. A SNRP of greater than 77 KW hrs/metric ton after disc refining described above generates a stock slurry that is difficult to drain from the fourdrinier wire. Specific Net Refiner Power is calculated by the following formula:
(Applied Power in Kilowatts to the refinerxe2x88x92the No Load Kilowatts)/(0.251*% consistency*flow rate in gpm*0.907 metric tons/ton).
For the formation of cellulose paper of sufficient smoothness, it is desirable to rewet the paper surface prior final calendering. Papers made on the paper machine with a high moisture content calendar much more readily than papers of the same moisture content containing water added in a remoistening operation. This is due to a partial irreversibility in the imbition of water by cellulose. However, calendering a paper with high moisture content results in blackening, a condition of transparency resulting from fibers in contact with each other being crushed. The crushed areas reflect less light and therefore appear dark, a condition that is undesirable in an imaging application such as a base for color paper. By adding moisture to the surface of the paper after the paper has been machine dried the problem of blackening can be avoided while preserving the advantages of high moisture calendering. The addition of surface moisture prior to machine calendering is intended to soften the surface fibers and not the fibers in the interior of the paper. Papers calendered with a high surface moisture content generally show greater strength, density, gloss and processing chemistry resistance, all of which are desirable for an imaging support and have been shown to be perceptually preferred to prior art photographic paper bases.
There are several paper surface humidification/moisturization techniques. The application of water, either by mechanical roller or aerosol mist by way of a electrostatic field, are two techniques known in the art. The above techniques require dwell time, hence web length, for the water to penetrate the surface and equalize in the top surface of the paper. Therefore, it is difficult for these above systems to make moisture corrections without distorting, spotting, and swelling of the paper. The preferred method to rewet the paper surface prior final calendering is by use of a steam application device. A steam application device uses saturated steam in a controlled atmosphere to cause water vapor to penetrate the surface of the paper and condense. Prior to calendering, the steam application device allows a considerable improvement in gloss and smoothness due to the heating up and moisturizing the paper of this invention before the pressure nip of the calendering rolls. An example of a commercially available system that allows for controlled steam moisturization of the surface of cellulose paper is the xe2x80x9cFluidex Systemxe2x80x9d manufactured by Pagendarm Corp. A preferred steam application or steam shower apparatus is the STEAM-FOIL of Thermo Electron Web System Incorporated.
For imaging supports, the use of a steam on the face side of the paper only is preferred since improved surface smoothness has commercial value for the imaging side of the paper. Application of the steam foil to both sides of the paper, while feasible, is unnecessary and adds additional cost to the product.
The preferred moisture content by weight after applying the steam and calendering is between 7% and 9%. A moisture level less than 7% is more costly to manufacture since more fiber is needed to reach a final basis weight. At a moisture level greater than 10% the surface of the paper begins to degrade. After the steam foil rewetting of the paper surface, the paper is calendered before winding of the paper. The preferred temperature of the calender rolls is between 76xc2x0 C. and 88xc2x0 C. Lower temperatures result in a poor surface. Higher temperatures are unnecessary as they do not improve the paper surface and require more energy.
Because the development of the silver halide imaging layers required submersion into wet processing chemistry, a water resistant coating applied to the paper is preferred as the coating protects the cellulose paper from the wet development chemistry and improves the strength of the paper during the wet processing of the image layers. The preferred methods for providing a water resistant layer are melt cast polyolefin polymers, laminated polyolefin sheets and laminated polyester sheets.
The pre-formed voided polymer sheet preferably is an oriented polymer because of the strength and toughness developed in the orientation process. Preferred polymers for the flexible substrate include polyolefins, polyester and nylon. Preferred polyolefms include polypropylene, polyethylene, polymethylpentene, polystyrene, polybutylene, and mixtures thereof. Polyolefin copolymers, including copolymers of propylene and ethylene such as hexene, butene, and octene are also useful. Polyolefins are preferred, as they are low in cost and have the desirable strength and toughness properties required for a pressure sensitive label. Oriented polymer sheet have been shown to improve the tear resistance of the base material, reduce the curl of the image element and are generally capable of providing improved image sharpness and brightness compared to melt cast polymers. Examples of preferred biaxially oriented polymer sheet are disclosed in U.S. Pat. Nos. 5,866,282; 5,853,965; 5,874,205; 5,888,643; 5,888,683; 5,902,720 and 5,935,690. Further, the biaxially oriented sheets preferably laminated to cellulose paper, which are high in strength, have tear resistance greater than 150 N.
When white pigments are added to an oriented polymer layer the polymer layer preferably includes a stabilizing amount of hindered amine extruded on the top side of the imaging layer substrate. Hindered amine light stabilizers (HALS) originate from 2,2,6,6-tetramethylpiperidine. The hindered amine should be added to the polymer layer at about 0.01-5% by weight of said resin layer in order to provide resistance to polymer degradation upon exposure to UV light. The preferred amount is at about 0.05-3% by weight. This provides excellent polymer stability and resistance to cracking and yellowing while keeping the expense of the hindered amine to a minimum. Examples of suitable hindered amines with molecular weights of less than 2300 are Bis(2,2,6,6-letramethyl-4-piperidinyl)sebacate; Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate and Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)2-n-butyl-(3,5-di-tert-butyl-hydroxy-benzyl)malonate.
Polyester polymers for the voided sheet of the invention are preferred as the mechanical modulus of polyester is higher than that of polyolefin polymers resulting in a stiffer, more durable image element. Further, it has been shown that higher amounts of white pigments can be added to polyester compared to polyolefin polymer, thus allowing additional improvements in image sharpness, whiteness and silver halide printing speed. Suitable dibasic acids useful for the preparation of polyesters include those containing from two to sixteen carbon atoms such as adipic acid, sebacic acid, isophthalic acid, terephthalic acid, and the like. Alkyl esters of acids such as those listed above can also be employed. Other alcohols and acids as well as polyesters prepared therefrom and the preparation of the polyesters are described in U.S. Pat. Nos. 2,720,503 and 2,901,466.
When using a cellulose fiber paper support, it is preferable to extrusion laminate the oriented polymer sheets to the base paper using a polyolefin resin. Extrusion laminating is carried out by bringing together the biaxially oriented sheets of the invention and the base paper with application of an adhesive between them followed by their being pressed in a nip such as between two rollers. The adhesive may be applied to either the biaxially oriented sheets or the base paper prior to their being brought into the nip. In a preferred form the adhesive is applied into the nip simultaneously with the biaxially oriented sheets and the base paper. The adhesive may be any suitable material that does not have a harmful effect upon the photographic element. A preferred material is polyethylene that is melted at the time it is placed into the nip between the paper and the biaxially oriented sheet.
In addition of white reflective water resistant layers to the cellulose paper of the invention, a waterproof layer that has a spectral transmission of between 40 and 70% is preferred. A spectral transmission between 40% and 70% is preferred as the silver halide formed image can be utilized as a transmission display product. This addition of calcium carbonate to the paper has been shown to better reduce light scattering and unwanted absorption compared to prior art paper which utilize TiO2 in the paper. Spectral transmission is the ratio of the transmitted power to the incident power and is expressed as a percentage as follows; TRGB=10xe2x88x92D*100 where D is the average of the red, green and blue Status A transmission density response measured by an X-Rite model 310 (or comparable) photographic transmission densitometer.
During the lamination process, it is desirable to maintain control of the tension of the biaxially oriented sheet(s) in order to minimize curl in the resulting laminated support. For high humidity applications ( greater than 50% RH) and low humidity applications ( less than 20% RH), it is desirable to laminate both a front side and back side film to keep curl to a minimum. Also, during the lamination process, it is desirable to laminate the top sheet to the face side of the paper. Generally, the face side of the paper is a smoother surface than the wire side. Lamination of the top sheet to the face side of the paper will generally yield a image with better gloss than lamination of the top sheet to the wire side of the paper.
As used herein the phrase xe2x80x9cimaging elementxe2x80x9d is a material that may be used as a imaging support for the transfer of images to the support by techniques such as ink jet printing, thermal dye transfer or electrophotographic printing as well as a support for silver halide images. As used herein, the phrase xe2x80x9cphotographic elementxe2x80x9d is a material that utilizes photosensitive silver halide in the formation of images. The thermal dye image-receiving layer of the receiving elements of the invention may comprise, for example, a polycarbonate, a polyurethane, a polyester, polyvinyl chloride, poly(styrene-co-acrylonitrile), poly(caprolactone) or mixtures thereof The dye image-receiving layer may be present in any amount which is effective for the intended purpose. In general, good results have been obtained at a concentration of from about 1 to about 10 g/m2. An overcoat layer may be further coated over the dye-receiving layer, such as described in U.S. Pat. No. 4,775,657 of Harrison et al.
Dye-donor elements that are used with the dye-receiving element of the invention conventionally comprise a support having thereon a dye containing layer. Any dye can be used in the dye-donor employed in the invention provided it is transferable to the dye-receiving layer by the action of heat. Especially good results have been obtained with sublimable dyes. Dye donors applicable for use in the present invention are described, e.g., in U.S. Pat. Nos. 4,916,112; 4,927,803 and 5,023,228.
As noted above, dye-donor elements are used to form a dye transfer image. Such a process comprises image-wise-heating a dye-donor element and transferring a dye image to a dye-receiving element as described above to form the dye transfer image.
In a preferred embodiment of the thermal dye transfer method of printing, a dye donor element is employed which compromises a poly-(ethylene terephthalate) support coated with sequential repeating areas of cyan, magenta, and yellow dye, and the dye transfer steps are sequentially performed for each color to obtain a three-color dye transfer image. Of course, when the process is only performed for a single color, then a monochrome dye transfer image is obtained.
Thermal printing heads which can be used to transfer dye from dye-donor elements to receiving elements of the invention are available commercially. There can be employed, for example, a Fujitsu Thermal Head (FT-040 MCS001), a TDK Thermal Head F415 HH7-1089 or a Rohm Thermal Head KE 2008-F3. Alternatively, other known sources of energy for thermal dye transfer may be used, such as lasers as described in, for example, GB No. 2,083,726A.
A thermal dye transfer assemblage of the invention comprises (a) a dye-donor element, and (b) a dye-receiving element as described above, the dye-receiving element being in a superposed relationship with the dye-donor element so that the dye layer of the donor element is in contact with the dye image-receiving layer of the receiving element.
When a three-color image is to be obtained, the above assemblage is formed on three occasions during the time when heat is applied by the thermal printing head. After the first dye is transferred, the elements are peeled apart. A second dye-donor element (or another area of the donor element with a different dye area) is then brought in register with the dye-receiving element and the process repeated. The third color is obtained in the same manner.
The electrographic and electrophotographic processes and their individual steps have been well described in detail in many books and publications. The processes incorporate the basic steps of creating an electrostatic image, developing that image with charged, colored particles (toner), optionally transferring the resulting developed image to a secondary substrate, and fixing the image to the substrate. There are numerous variations in these processes and basic steps; the use of liquid toners in place of dry toners is simply one of those variations.
The first basic step, creation of an electrostatic image, can be accomplished by a variety of methods. The electrophotographic process of copiers uses imagewise photodischarge, through analog or digital exposure, of a uniformly charged photoconductor. The photoconductor may be a single-use system, or it may be rechargeable and reimageable, like those based on selenium or organic photorecptors.
One form of the electrophotographic process of copiers uses imagewise photodischarge, through analog or digital exposure, of a uniformly charged photoconductor. The photoconductor may be a single-use system, or it may be rechargeable and reimageable, like those based on selenium or organic photoreceptors.
In an alternate electrographic process, electrostatic images are created ionographically. The latent image is created on dielectric (charge-holding) medium, either paper or film. Voltage is applied to selected metal styli or writing nibs from an array of styli spaced across the width of the medium, causing a dielectric breakdown of the air between the selected styli and the medium. Ions are created, which form the latent image on the medium.
Electrostatic images, however generated, are developed with oppositely charged toner particles. For development with liquid toners, the liquid developer is brought into direct contact with the electrostatic image. Usually a flowing liquid is employed, to ensure that sufficient toner particles are available for development. The field created by the electrostatic image causes the charged particles, suspended in a nonconductive liquid, to move by electrophoresis. The charge of the latent electrostatic image is thus neutralized by the oppositely charged particles. The theory and physics of electrophoretic development with liquid toners are well described in many books and publications.
If a reimageable photoreceptor or an electrographic master is used, the toned image is transferred to paper (or other substrate). The paper is charged electrostatically, with the polarity chosen to cause the toner particles to transfer to the paper. Finally, the toned image is fixed to the paper. For self-fixing toners, residual liquid is removed from the paper by air-drying or heating. Upon evaporation of the solvent these toners form a film bonded to the paper. For heatfusible toners, thermoplastic polymers are used as part of the particle. Heating both removes residual liquid and fixes the toner to paper.
Ink jet images are preferred to provide a digital printing method that can be utilized in the home. The dye receiving layer or DRL for ink jet imaging may be applied by any known methods. Such as solvent coating, or melt extrusion coating techniques. The DRL is coated over the tie layer (TL) at a thickness ranging from 0.1-10 xcexcm, preferably 0.5-5 xcexcm. There are many known formulations which may be useful as dye receiving layers. The primary requirement is that the DRL is compatible with the inks which it will be imaged so as to yield the desirable color gamut and density. As the ink drops pass through the DRL, the dyes are retained or mordanted in the DRL, while the ink solvents pass freely through the DRL and are rapidly absorbed by the TL. Additionally, the DRL formulation is preferably coated from water, exhibits adequate adhesion to the TL, and allows for easy control of the surface gloss.
For example, Misuda et al. in U.S. Pat. Nos. 4,879,166; 5,264,275; 5,104,730; 4,879,166, and Japanese patents 1,095,091; 2,276,671; 2,276,670; 4,267,180; 5,024,335; and 5,016,517 discloses aqueous based DRL formulations comprising mixtures of psuedo-bohemite and certain water soluble resins. Light, in U.S. Pat. Nos. 4,903,040; 4,930,041; 5,084,338; 5,126,194; 5,126,195; and 5,147,717 discloses aqueous-based DRL formulations comprising mixtures of vinyl pyrrolidone polymers and certain water-dispersible and/or water-soluble polyesters, along with other polymers and addenda. Butters et al. in U.S. Pat. Nos. 4,857,386 and 5,102,717 disclose ink-absorbent resin layers comprising mixtures of vinyl pyrrolidone polymers and acrylic or methacrylic polymers. Sato et al. in U.S. Pat. No. 5,194,317 and Higuma et al. in U.S. Pat. No. 5,059,983 disclose aqueous-coatable DRL formulations based on poly (vinyl alcohol). Iqbal, in U.S. Pat. No. 5,208,092, discloses water-based DRL formulations comprising vinyl copolymers which are subsequently cross-linked. In addition to these examples, there may be other known or contemplated DRL formulations which are consistent with the aforementioned primary and secondary requirements of the DRL, all of which fall under the spirit and scope of the current invention.
The preferred DRL is a 0.1-10 micrometers DRL which is coated as an aqueous dispersion of 5 parts alumoxane and 5 parts poly (vinyl pyrrolidone). The DRL may also contain varying levels and sizes of matting agents for the purpose of controlling gloss, friction, and/or finger print resistance, surfactants to enhance surface uniformity and to adjust the surface tension of the dried coating, mordanting agents, anti-oxidants, UV absorbing compounds, light stabilizers, and the like.
Although the ink-receiving elements as described above can be successfully used to achieve the objectives of the present invention, it may be desirable to overcoat the DRL for the purpose of enhancing the durability of the imaged element. Such overcoats may be applied to the DRL either before or after the element is imaged. For example, the DRL can be overcoated with an inkpermeable layer through which inks freely pass. Layers of this type are described in U.S. Pat. Nos. 4,686,118; 5,027,131; and 5,102,717. Alternatively, an overcoat may be added after the element is imaged. Any of the known laminating films and equipment may be used for this purpose. The inks used in the aforementioned imaging process are well known, and the ink formulations are often closely tied to the specific processes, i.e., continuous, piezoelectric, or thermal. Therefore, depending on the specific ink process, the inks may contain widely differing amounts and combinations of solvents, colorants, preservatives, surfactants, humectants, and the like. Inks preferred for use in combination with the image recording elements of the present invention are water-based, such as those currently sold for use in the Hewlett-Packard Desk Writer 560C printer. However, it is intended that alternative embodiments of the image-recording elements as described above, which may be formulated for use with inks which are specific to a given ink-recording process or to a given commercial vendor, fall within the scope of the present invention.
Nacreous silver halide images are sometimes preferred as they provide both a nacreous appearance as well as photographic dye purity. This invention in one embodiment is directed to a silver halide photographic element capable of excellent performance when exposed by either an electronic printing method or a conventional optical printing method. An electronic printing method comprises subjecting a radiation sensitive silver halide emulsion layer of a recording element to actinic radiation of at least 10xe2x88x924 ergs/cm2 for up to 100xcexc seconds duration in a pixel-by-pixel mode wherein the silver halide emulsion layer is comprised of silver halide grains as described above. A conventional optical printing method comprises subjecting a radiation sensitive silver halide emulsion layer of a recording element to actinic radiation of at least 10xe2x88x924 ergs/cm2 for 10xe2x88x923 to 300 seconds in an imagewise mode wherein the silver halide emulsion layer is comprised of silver halide grains as described above.
This invention in a preferred embodiment utilizes a radiationsensitive emulsion comprised of silver halide grains (a) containing greater than 50 mole percent chloride, based on silver, (b) having greater than 50 percent of their surface area provided by {100} crystal faces, and (c) having a central portion accounting for from 95 to 99 percent of total silver and containing two dopants selected to satisfy each of the following class requirements: (i) a hexacoordination metal complex which satisfies the formula:
[ML6]Rxe2x80x83xe2x80x83(I)
wherein n is zero, xe2x88x921, xe2x88x922, xe2x88x923 or xe2x88x924; M is a filled frontier orbital polyvalent metal ion, other than iridium; and L represents bridging ligands which can be independently selected, provided that least four of the ligands are anionic ligands, and at least one of the ligands is a cyano ligand or a ligand more electronegative than a cyano ligand; and (ii) an iridium coordination complex containing a thiazole or substituted thiazole ligand.
This invention is directed towards a photographic recording element comprising a support and at least one light sensitive silver halide emulsion layer comprising silver halide grains as described above.
It has been discovered quite surprisingly that the combination of dopants (i) and (ii) provides greater reduction in reciprocity law failure than can be achieved with either dopant alone. Further, unexpectedly, the combination of dopants (i) and (ii) achieve reductions in reciprocity law failure beyond the simple additive sum achieved when employing either dopant class by itself. It has not been reported or suggested prior to this invention that the combination of dopants (i) and (ii) provides greater reduction in reciprocity law failure, particularly for high intensity and short duration exposures. The combination of dopants (i) and (ii) further unexpectedly achieves high intensity reciprocity with iridium at relatively low levels, and both high and low intensity reciprocity improvements even while using conventional gelatino-peptizer (e.g., other than low methionine gelatino-peptizer).
In a preferred practical application, the advantages of the invention can be transformed into increased throughput of digital substantially artifact-free color print images while exposing each pixel sequentially in synchronism with the digital data from an image processor.
In one embodiment, the present invention represents an improvement on the electronic printing method. Specifically, this invention in one embodiment is directed to an electronic printing method which comprises subjecting a radiation sensitive silver halide emulsion layer of a recording element. to actinic radiation of at least 10xe2x88x924 ergs/cm2 for up to 100xcexc seconds duration in a pixel-by-pixel mode. The present invention realizes an improvement in reciprocity failure by selection of the radiation sensitive silver halide emulsion layer. While certain embodiments of the invention are specifically directed towards electronic printing, use of the emulsions and elements of the invention is not limited to such specific embodiment, and it is specifically contemplated that the emulsions and elements of the invention are also well suited for conventional optical printing.
It has been formed that significantly improved reciprocity performance can be obtained for silver halide grains (a) containing greater than 50 mole percent chloride, based on silver, and (b) having greater than 50 percent of their surface area provided by {100} crystal faces by employing a hexacoordination complex dopant of class (i) in combination with an iridium complex dopant comprising a thiazole or substituted thiazole ligand. The reciprocity improvement is obtained for silver halide grains employing conventional gelatino-peptizer, unlike the contrast improvement described for the combination of dopants set forth in U.S. Pat. Nos. 5,783,373 and 5,783,378, which requires the use of low methionine gelatino-peptizers as discussed therein, and which states it is preferable to limit the concentration of any gelatino-peptizer with a methionine level of greater than 30 micromoles per gram to a concentration of less than 1 percent of the total peptizer employed. Accordingly, in specific embodiments of the invention, it is specifically contemplated to use significant levels (i.e., greater than 1 weight percent of total peptizer) of conventional gelatin (e.g., gelatin having at least 30 micromoles of methionine per gram) as a gelatinopeptizer for the silver halide grains of the emulsions of the invention. In preferred embodiments of the invention, gelatino-peptizer is employed which comprises at least 50 weight percent of gelatin containing at least 30 micromoles of methionine per gram, as it is frequently desirable to limit the level of oxidized low methionine gelatin which may be used for cost and certain performance reasons.
In a specific, preferred form of the invention it is contemplated to employ a class (i) hexacoordination complex dopant satisfying the formula:
[ML6]Rxe2x80x83xe2x80x83(I)
where
n is zero, xe2x88x921, xe2x88x922, xe2x88x923 or xe2x88x924;
M is a filled frontier orbital polyvalent metal ion, other than iridium, preferably Fe+2, Ru+2, Os+2, Co+3, Rh+3, Pd+4 or Pt+4, more preferably an iron, ruthenium or osmium ion, and most preferably a ruthenium ion;
L6 represents six bridging ligands which can be independently selected, provided that least four of the ligands are anionic ligands and at least one (preferably at least 3 and optimally at least 4) of the ligands is a cyano ligand or a ligand more electronegative than a cyano ligand. Any remaining ligands can be selected from among various other bridging ligands, including aquo ligands, halide ligands (specifically, fluoride, chloride, bromide and iodide), cyanate ligands, thiocyanate ligands, selenocyanate ligands, tellurocyanate ligands, and azide ligands. Hexacoordinated transition metal complexes of class (i) which include six cyano ligands are specifically preferred.
Illustrations of specifically contemplated class (i) hexacoordination complexes for inclusion in the high chloride grains are provided by Olm et al U.S. Pat. No. 5,503,970 and Daubendiek et al U.S. Pat. Nos. 5,494,789 and 5,503,971, and Keevert et al U.S. Pat. No. 4,945,035, as well as Murakami et al Japanese Patent Application Hei-2[1990]-249588, and Research Disclosure Item 36736. Useful neutral and anionic organic ligands for class (ii) dopant hexacoordination complexes are disclosed by Olm et al U.S. Pat. No. 5,360,712 and Kuromoto et al U.S. Pat. No. 5,462,849.
Class (i) dopant is preferably introduced into the high chloride grains after at least 50 (most preferably 75 and optimally 80) percent of the silver has been precipitated, but before precipitation of the central portion of the grains has been completed. Preferably class (i) dopant is introduced before 98 (most preferably 95 and optimally 90) percent of the silver has been precipitated. Stated in terms of the fully precipitated grain structure, class (i) dopant is preferably present in an interior shell region that surrounds at least 50 (most preferably 75 and optimally 80) percent of the silver and, with the more centrally located silver, accounts the entire central portion (99 percent of the silver), most preferably accounts for 95 percent, and optimally accounts for 90 percent of the silver halide forming the high chloride grains. The class (i) dopant can be distributed throughout the interior shell region delimited above or can be added as one or more bands within the interior shell region.
Class (i) dopant can be employed in any conventional useful concentration. A preferred concentration range is from 10xe2x88x928 to 10xe2x88x923 mole per silver mole, most preferably from 10xe2x88x926to 5xc3x9710xe2x88x924 mole per silver mole.
The following are specific illustrations of class (i) dopants:
(i-1) [Fe(CN)6]xe2x88x924 
(i-2) [Ru(CN)6]xe2x88x924 
(i-3) [Os(CN)6]xe2x88x924 
(i-4) [Rh(CN)6]xe2x88x923 
(i-5) [Co(CN)6]xe2x88x923 
(i-6) [Fe(pyrazine)(CN)5]xe2x88x924 
(i-7) [RuCl(CN)5]xe2x88x924 
(i-8) [OsBr(CN)5]xe2x88x924 
(i-9) [RhF(CN)5]xe2x88x923 
(i-10) [In(NCS)6]xe2x88x923 
(i-11) [FeCO(CN)5]xe2x88x923 
(i-12) [RuF2(CN)4]xe2x88x924 
(i-13) [OsCl2(CN)4]xe2x88x924 
(i-14) [RhI2(CN)4]xe2x88x923 
(i-15) [Ga(NCS)6]3 
(i-16) [Ru(CN)5(OCN)]xe2x88x924 
(i-17) [Ru(CN)5(N3)]xe2x88x924 
(i-18) [Os(CN)5(SCN)]xe2x88x924 
(i-19) [Rh(CN)5(SeCN)]xe2x88x923 
(i-20) [Os(CN)Cl5]xe2x88x924 
(i-21) [Fe(CN)3Cl3]xe2x88x923 
(i-22) [Ru(CO)2(CN)4]xe2x88x921 
When the class (i) dopants have a net negative charge, it is appreciated that they are associated with a counter ion when added to the reaction vessel during precipitation. The counter ion is of little importance, since it is ionically dissociated from the dopant in solution and is not incorporated within the grain. Common counter ions known to be fully compatible with silver chloride precipitation, such as ammonium and alkali metal ions, are contemplated. It is noted that the same comments apply to class (ii) dopants, otherwise described below.
The class (ii) dopant is an iridium coordination complex containing at least one thiazole or substituted thiazole ligand. Careful scientific investigations have revealed Group VIII hexahalo coordination complexes to create deep electron traps, as illustrated R. S. Eachus, R. E. Graves and M. T. Olm J. Chem. Phys., Vol. 69, pp. 4580-7 (1978) and Physica Status SolidiA, Vol. 57, 429-37 (1980) and R. S. Eachus and M. T. Olm Annu. Rep. Prog. Chem. Sect. C. Phys. Chem., Vol. 83, 3, pp. 3-48 (1986). The class (ii) dopants employed in the practice of this invention are believed to create such deep electron traps. The thiazole ligands may be substituted with any photographically acceptable substituent which does not prevent incorporation of the dopant into the silver halide grain. Exemplary substituents include lower alkyl (e.g., alkyl groups containing 1-4 carbon atoms), and specifically methyl. A specific example of a substituted thiazole ligand which may be used in accordance with the invention is 5-methylthiazole. The class (ii) dopant preferably is an iridium coordination complex having ligands each of which are more electropositive than a cyano ligand. In a specifically preferred form the remaining non-thiazole or non-substituted-thiazole ligands of the coordination complexes forming class (ii) dopants are halide ligands.
It is specifically contemplated to select class (ii) dopants from among the coordination complexes containing organic ligands disclosed by Olm et al U.S. Pat. No. 5,360,712, Olm et al U.S. Pat. No. 5,457,021 and Kuromoto et al U.S. Pat. No. 5,462,849.
In a preferred form it is contemplated to employ as a class (ii) dopant a hexacoordination complex satisfying the formula:
[IrL16]nxe2x80x2xe2x80x83xe2x80x83(II)
wherein
nxe2x80x2 is zero, xe2x88x921, xe2x88x922, xe2x88x923 or xe2x88x924; and
L16 represents six bridging ligands which can be independently selected, provided that at least four of the ligands are anionic ligands, each of the ligands is more electropositive than a cyano ligand, and at least one of the ligands comprises a thiazole or substituted thiazole ligand. In a specifically preferred form at least four of the ligands are halide ligands, such as chloride or bromide ligands.
Class (ii) dopant is preferably introduced into the high chloride grains after at least 50 (most preferably 85 and optimally 90) percent of the silver has been precipitated, but before precipitation of the central portion of the grains has been completed. Preferably class (ii) dopant is introduced before 99 (most preferably 97 and optimally 95) percent of the silver has been precipitated. Stated in terms of the fully precipitated grain structure, class (ii) dopant is preferably present in an interior shell region that surrounds at least 50 (most preferably 85 and optimally 90) percent of the silver and, with the more centrally located silver, accounts the entire central portion (99 percent of the silver), most preferably accounts for 97 percent, and optimally accounts for 95 percent of the silver halide forming the high chloride grains. The class (ii) dopant can be distributed throughout the interior shell region delimited above or can be added as one or more bands within the interior shell region.
Class (ii) dopant can be employed in any conventional usefull concentration. A preferred concentration range is from 10xe2x88x929 to 10xe2x88x924 mole per silver mole. Iridium is most preferably employed in a concentration range of from 10xe2x88x928 to 10xe2x88x925 mole per silver mole.
Specific illustrations of class (ii) dopants are the following:
(ii-1) [IrCl5(thiazole)]xe2x88x922 
(ii-2) [IrCl4(thiazole)2]xe2x88x921 
(ii-3) [IrBr5(thiazole)]xe2x88x922 
(ii-4) [IrBr4(thiazole)2]xe2x88x921 
(ii-5) [IrCl5(5-methylthiazole)]xe2x88x922 
(ii-6) [IrCl4(5-methylthiazole)2]xe2x88x921 
(ii-7) [IrBr5(5-methylthiazole)]xe2x88x922 
(ii-8) [IrBr4(5-methylthiazole)2]xe2x88x921 
In one preferred aspect of the invention in a layer using a magenta dye forming coupler, a class (ii) dopant in combination with an OsCl5(NO) dopant has been found to produce a preferred result.
Emulsions demonstrating the advantages of the invention can be realized by modifying the precipitation of conventional high chloride silver halide grains having predominantly ( greater than 50%) {100} crystal faces by employing a combination of class (i) and (ii) dopants as described above.
The silver halide grains precipitated contain greater than 50 mole percent chloride, based on silver. Preferably the grains contain at least 70 mole percent chloride and, optimally at least 90 mole percent chloride, based on silver. Iodide can be present in the grains up to its solubility limit, which is in silver iodochloride grains, under typical conditions of precipitation, about 11 mole percent, based on silver. It is preferred for most photographic applications to limit iodide to less than 5 mole percent iodide, most preferably less than 2 mole percent iodide, based on silver.
Silver bromide and silver chloride are miscible in all proportions. Hence, any portion, up to 50 mole percent, of the total halide not accounted for chloride and iodide, can be bromide. For color reflection print (i.e., color paper) uses bromide is typically limited to less than 10 mole percent based on silver and iodide is limited to less than 1 mole percent based on silver.
In a widely used form high chloride grains are precipitated to form cubic grainsxe2x80x94that is, grains having {100} major faces and edges of equal length. In practice ripening effects usually round the edges and corners of the grains to some extent. However, except under extreme ripening conditions substantially more than 50 percent of total grain surface area is accounted for by {100} crystal faces.
High chloride tetradecahedral grains are a common variant of cubic grains. These grains contain 6 {100} crystal faces and 8 {111} crystal faces. Tetradecahedral grains are within the contemplation of this invention to the extent that greater than 50 percent of total surface area is accounted for by {100} crystal faces.
Although it is common practice to avoid or minimize the incorporation of iodide into high chloride grains employed in color paper, it is has been recently observed that silver iodochloride grains with {100} crystal faces and, in some instances, one or more {111} faces offer exceptional levels of photographic speed. In the these emulsions iodide is incorporated in overall concentrations of from 0.05 to 3.0 mole percent, based on silver, with the grains having a surface shell of greater than 50 xc3x85 that is substantially free of iodide and a interior shell having a maximum iodide concentration that surrounds a core accounting for at least 50 percent of total silver. Such grain structures are illustrated by Chen et al EPO 0 718 679.
In another improved form the high chloride grains can take the form of tabular grains having {100} major faces. Preferred high chloride {100} tabular grain emulsions are those in which the tabular grains account for at least 70 (most preferably at least 90) percent of total grain projected area. Preferred high chloride {100} tabular grain emulsions have average aspect ratios of at least 5 (most preferably at least  greater than 8). Tabular grains typically have thicknesses of less than 0.3 xcexcm, preferably less than 0.2 xcexcm, and optimally less than 0.07 xcexcm. High chloride {100} tabular grain emulsions and their preparation are disclosed by Maskasky U.S. Pat. Nos. 5,264,337 and 5,292,632, House et al U.S. Pat. No. 5,320,938, Brust et al U.S. Pat. No. 5,314,798 and Chang et al U.S. Pat. No. 5,413,904.
Once high chloride grains having predominantly {100} crystal faces have been precipitated with a combination of class (i) and class (ii) dopants described above, chemical and spectral sensitization, followed by the addition of conventional addenda to adapt the emulsion for the imaging application of choice can take any convenient conventional form. These conventional features are illustrated by Research Disclosure, Item 38957, cited above, particularly:
III. Emulsion washing;
IV. Chemical sensitization;
V. Spectral sensitization and desensitization;
VII. Antifoggants and stabilizers;
VIII. Absorbing and scattering materials;
IX. Coating and physical property modifying addenda; and
X. Dye image formers and modifiers.
Some additional silver halide, typically less than 1 percent, based on total silver, can be introduced to facilitate chemical sensitization. It is also recognized that silver halide can be epitaxially deposited at selected sites on a host grain to increase its sensitivity. For example, high chloride {100} tabular grains with corner epitaxy are illustrated by Maskasky U.S. Pat. No. 5,275,930. For the purpose of providing a clear demarcation, the term xe2x80x9csilver halide grainxe2x80x9d is herein employed to include the silver necessary to form the grain up to the point that the final {100} crystal faces of the grain are formed. Silver halide later deposited that does not overlie the {100} crystal faces previously formed accounting for at least 50 percent of the grain surface area is excluded in determining total silver forming the silver halide grains. Thus, the silver forming selected site epitaxy is not part of the silver halide grains while silver halide that deposits and provides the final {100} crystal faces of the grains is included in the total silver forming the grains, even when it differs significantly in composition from the previously precipitated silver halide.
Image dye-forming couplers may be included in the element such as couplers that form cyan dyes upon reaction with oxidized color developing agents which are described in such representative patents and publications as: U.S. Pat. Nos. 2,367,531; 2,423,730; 2,474,293; 2,772,162; 2,895,826; 3,002,836; 3,034,892; 3,041,236; 4,883,746 and xe2x80x9cFarbkuppler-Eine Literature Ubersicht,xe2x80x9d published in Agfa Mitteilungen, Band III, pp. 156-175 (1961). Preferably such couplers are phenols and naphthols that form cyan dyes on reaction with oxidized color developing agent. Also preferable are the cyan couplers described in, for instance, European Patent Application Nos. 491,197; 544,322; 556,700; 556,777; 565,096; 570,006; and 574,948.
Typical cyan couplers are represented by the following formulas: 
wherein R1, R5 and R8 each represents a hydrogen or a substituent; R2 represents a substituent; R3, R4 and R7 each represents an electron attractive group having a Hammett""s substituent constant "sgr"para of 0.2 or more and the sum of the "sgr"para values of R3 and R4 is 0.65 or more; R6 represents an electron attractive group having a Hammett""s substituent constant "sgr"apara of 0.35 or more; X represents a hydrogen or a coupling-off group; Z1 represents nonmetallic atoms necessary for forming a nitrogen-containing, six-membered, heterocyclic ring which has at least one dissociative group; Z2 represents xe2x80x94C(R7)xe2x95x90 and xe2x80x94Nxe2x95x90; and Z3 and Z4 each represents xe2x80x94C(R8xe2x95x90 and xe2x80x94Nxe2x95x90.
For purposes of this invention, an xe2x80x9cNB couplerxe2x80x9d is a dye-forming coupler which is capable of coupling with the developer 4-amino-3-methyl-N-ethyl-N-(2-methanesulfonamidoethyl) aniline sesquisulfate hydrate to form a dye for which the left bandwidth (LBW) of its absorption spectra upon xe2x80x9cspin coatingxe2x80x9d of a 3% w/v solution of the dye in di-n-butyl sebacate solvent is at least 5 nm. less than the LBW for a 3% w/v solution of the same dye in acetonitrile. The LBW of the spectral curve for a dye is the distance between the left side of the spectral curve and the wavelength of maximum absorption measured at a density of half the maximum.
The xe2x80x9cspin coatingxe2x80x9d sample is prepared by first preparing a solution of the dye in di-n-butyl sebacate solvent (3% w/v). If the dye is insoluble, dissolution is achieved by the addition of some methylene chloride. The solution is filtered and 0.1-0.2ml is applied to a clear polyethylene terephthalate support (approximately 4 cmxc3x974 cm) and spun at 4,000 RPM using the Spin Coating equipment, Model No. EC101, available from Headway Research Inc., Garland Tex. The transmission spectra of the so prepared dye samples are then recorded.
Preferred xe2x80x9cNB couplersxe2x80x9d form a dye which, in n-butyl sebacate, has a LBW of the absorption spectra upon xe2x80x9cspin coatingxe2x80x9d which is at least 15 nm, preferably at least 25 nm, less than that of the same dye in a 3% solution (w/v) in acetonitrile.
In a preferred embodiment the cyan dye-forming xe2x80x9cNB couplerxe2x80x9d useful in the invention has the formula (IA) 
wherein
Rxe2x80x2 and Rxe2x80x3 are substituents selected such that the coupler is a xe2x80x9cNB couplerxe2x80x9d, as herein defined; and
Z is a hydrogen atom or a group which can be split off by the reaction of the coupler with an oxidized color developing agent.
The coupler of formula (IA) is a 2,5-diamido phenolic cyan coupler wherein the substituents Rxe2x80x2 and Rxe2x80x3 are preferably independently selected from unsubstituted or substituted alky, aryl, amino, alkoxy and heterocyclyl groups.
In a further preferred embodiment, the xe2x80x9cNB couplerxe2x80x9d has the formula (1): 
wherein
Rxe2x80x3 and Rxe2x80x2xe2x80x3 are independently selected from unsubstituted or substituted alkyl, aryl, amino, alkoxy and heterocyclyl groups and Z is as hereinbefore defined;
R1 and R2 are independently hydrogen or an unsubstituted or substituted alkyl group; and
Typically, Rxe2x80x3 is an alkyl, amino or aryl group, suitably a phenyl group. Rxe2x80x2xe2x80x3 is desirably an alkyl or aryl group or a 5-10 membered heterocyclic ring which contains one or more heteroatoms selected from nitrogen, oxygen and sulfur, which ring group is unsubstituted or substituted.
In the preferred embodiment the coupler of formula (I) is a 2,5-diamido phenol in which the 5-amido moiety is an amide of a carboxylic acid which is substituted in the alpha position by a particular sulfone (xe2x80x94SO2xe2x80x94) group, such as, for example, described in U.S. Pat. No. 5,686,235. The sulfone moiety is an unsubstituted or substituted alkylsulfone or a heterocyclyl sulfone or it is an arylsulfone, which is preferably substituted, in particular in the meta and/or para position.
Couplers having these structures of formulae (I) or (IA) comprise cyan dye-forming xe2x80x9cNB couplersxe2x80x9d which form image dyes having very sharp-cutting dye hues on the short wavelength side of the absorption curves with absorption maxima (xcexmax) which are shifted hypsochromically and are generally in the range of 620-645 nm, which is ideally suited for producing excellent color reproduction and high color saturation in color photographic papers.
Referring to formula (I), R1 and R2 are independently hydrogen or an unsubstituted or substituted alkyl group, preferably having from 1 to 24 carbon atoms and in particular 1 to 10 carbon atoms, suitably a methyl, ethyl, n-propyl, isopropyl, butyl or decyl group or an alkyl group substituted with one or more fluoro, chloro or bromo atoms, such as a trifluoromethyl group. Suitably, at least one of R1 and R2 is a hydrogen atom and if only one of R1 and R2 is a hydrogen atom then the other is preferably an alkyl group having 1 to 4 carbon atoms, more preferably one to three carbon atoms and desirably two carbon atoms.
As used herein and throughout the specification unless where specifically stated otherwise, the term xe2x80x9calkylxe2x80x9d refers to an unsaturated or saturated straight or branched chain alkyl group, including alkenyl, and includes aralkyl and cyclic alkyl groups, including cycloalkenyl, having 3-8 carbon atoms and the term xe2x80x98arylxe2x80x99 includes specifically fused aryl.
In formula (I), Rxe2x80x3 is suitably an unsubstituted or substituted amino, alkyl or aryl group or a 5-10 membered heterocyclic ring which contains one or more heteroatoms selected from nitrogen, oxygen and sulfur, which ring is unsubstituted or substituted, but is more suitably an unsubstituted or substituted phenyl group.
Examples of suitable substituent groups for this aryl or heterocyclic ring include cyano, chloro, fluoro, bromo, iodo, alkyl- or aryl-carbonyl, alkyl- or aryl-oxycarbonyl, carbonamido, alkyl- or aryl-carbonamido, alkyl- or aryl-sulfonyl, alkyl- or aryl-sulfonyloxy, alkyl- or aryl-oxysulfonyl, alkyl- or aryl-sulfoxide, alkyl- or aryl-sulfamoyl, alkyl- or aryl-sulfonamido, aryl, alkyl, alkoxy, aryloxy, nitro, alkyl- or aryl-ureido and alkyl- or aryl-carbamoyl groups, any of which may be further substituted. Preferred groups are halogen, cyano, alkoxycarbonyl, alkylsulfamoyl, alkyl-sulfonamido, alkylsulfonyl, carbamoyl, alkylcarbamoyl or alkylcarbonamido. Suitably, Rxe2x80x3 is a 4-chlorophenyl, 3,4-dichlorophenyl, 3,4difluorophenyl, 4-cyanophenyl, 3-chloro-4-cyanophenyl, pentafluorophenyl, or a 3- or 4-sulfonamidophenyl group.
In formula (I), when Rxe2x80x2xe2x80x3 is alkyl it may be unsubstituted or substituted with a substituent such as halogen or alkoxy. When Rxe2x80x2xe2x80x3 is aryl or a heterocycle, it may be substituted. Desirably it is not substituted in the position alpha to the sulfonyl group.
In formula (I), when Rxe2x80x2xe2x80x3 is a phenyl group, it may be substituted in the meta and/or para positions with one to three substituents independently selected from the group consisting of halogen, and unsubstituted or substituted alkyl, alkoxy, aryloxy, acyloxy, acylamino, alkyl- or aryl-sulfonyloxy, alkyl- or aryl-sulfamoyl, alkyl- or aryl-sulfamoylamino, alkyl- or aryl-sulfonamido, alkyl- or aryl-ureido, alkyl- or aryl-oxycarbonyl, alkyl- or aryl-oxycarbonylamino and alkyl- or aryl-carbamoyl groups.
In particular each substituent may be an alkyl group such as methyl, t-butyl, heptyl, dodecyl, pentadecyl, octadecyl or 1,1,2,2-tetramethylpropyl; an alkoxy group such as methoxy, t-butoxy, octyloxy, dodecyloxy, tetradecyloxy, hexadecyloxy or octadecyloxy; an aryloxy group such as phenoxy, 4-t-butylphenoxy or 4-dodecyl-phenoxy; an alkyl- or aryl-acyloxy group such as acetoxy or dodecanoyloxy; an alkyl- or aryl-acylamino group such as acetamido, hexadecanamido or benzamido; an alkyl- or aryl-sulfonyloxy group such as methyl-sulfonyloxy, dodecylsulfonyloxy or 4-methylphenyl-sulfonyloxy; an alkyl- or aryl-sulfamoyl-group such as N-butylsulfamoyl or N-4-t-butylphenylsulfamoyl; an alkyl- or aryl-sulfamoylamino group such as N-butylsulfamoylamino or N-4-t-butylphenylsulfamoyl-amino; an alkyl- or aryl-sulfonamido group such as methane-sulfonamido, hexadecanesulfonamido or 4-chlorophenyl-sulfonamido; an alkyl- or aryl-ureido group such as methylureido or phenylureido; an alkoxy- or aryloxy-carbonyl such as methoxycarbonyl or phenoxycarbonyl; an alkoxy- or aryloxy-carbonylamino group such as methoxycarbonylamino or phenoxycarbonylamino; an alkyl- or aryl-carbamoyl group such as N-butylcarbamoyl or N-methyl-N-dodecylcarbamoyl; or a perfluoroalkyl group such as trifluoromethyl or heptafluoropropyl.
Suitably the above substituent groups have 1 to 30 carbon atoms, more preferably 8 to 20 aliphatic carbon atoms. A desirable substituent is an alkyl group of 12 to 18 aliphatic carbon atoms such as dodecyl, pentadecyl or octadecyl or an alkoxy group with 8 to 18 aliphatic carbon atoms such as dodecyloxy and hexadecyloxy or a halogen such as a meta or para chloro group, carboxy or sulfonamido. Any such groups may contain interrupting heteroatoms such as oxygen to form e.g. polyalkylene oxides.
In formula (I) or (IA) Z is a hydrogen atom or a group which can be split off by the reaction of the coupler with an oxidized color developing agent, known in the photographic art as a xe2x80x98coupling-off groupxe2x80x99 and may preferably be hydrogen, chloro, fluoro, substituted aryloxy or mercaptotetrazole, more preferably hydrogen or chloro.
The presence or absence of such groups determines the chemical equivalency of the coupler, i.e., whether it is a 2-equivalent or 4-equivalent coupler, and its particular identity can modify the reactivity of the coupler. Such groups can advantageously affect the layer in which the coupler is coated, or other layers in the photographic recording material, by performing, after release from the coupler, functions such as dye formation, dye hue adjustment, development acceleration or inhibition, bleach acceleration or inhibition, electron transfer facilitation, color correction, and the like.
Representative classes of such coupling-off groups include, for example, halogen, alkoxy, aryloxy, heterocyclyloxy, sulfonyloxy, acyloxy, acyl, heterocyclylsulfonamido, heterocyclylthio, benzothiazolyl, phosophonyloxy, alkylthio, arylthio, and arylazo. These coupling-off groups are described in the art, for example, in U.S. Pat. Nos. 2,455,169; 3,227,551; 3,432,521; 3,467,563; 3,617,291; 3,880,661; 4,052,212; and 4,134,766; and in U.K. Patent Nos. and published applications 1,466,728; 1,531,927; 1,533,039; 2,066,755A, and 2,017,704A. Halogen, alkoxy, and aryloxy groups are most suitable.
Examples of specific coupling-off groups are xe2x80x94Cl, xe2x80x94F, xe2x80x94Br, xe2x80x94SCN, xe2x80x94OCH3, xe2x80x94OC6H5, xe2x80x94OCH2C(xe2x95x90O)NHCH2CH2OH, xe2x80x94OCH2C(O)NHCH2CH2OCH3, xe2x80x94OCH2C(O)NHCH2CH2OC(xe2x95x90O)OCH3, xe2x80x94P(xe2x95x90O)(OC2H5)2, xe2x80x94SCH2CH2COOH, 
Typically, the coupling-off group is a chlorine atom, hydrogen atom or p-methoxyphenoxy group.
It is essential that the substituent groups be selected so as to adequately ballast the coupler and the resulting dye in the organic solvent in which the coupler is dispersed. The ballasting may be accomplished by providing hydrophobic substituent groups in one or more of the substituent groups. Generally a ballast group is an organic radical of such size and configuration as to confer on the coupler molecule sufficient bulk and aqueous insolubility as to render the coupler substantially nondiffusible from the layer in which it is coated in a photographic element. Thus the combination of substituent are suitably chosen to meet these criteria To be effective, the ballast will usually contain at least 8 carbon atoms and typically contains 10 to 30 carbon atoms. Suitable ballasting may also be accomplished by providing a plurality of groups which in combination meet these criteria. In the preferred embodiments of the invention R1 in formula (I) is a small alkyl group or hydrogen. Therefore, in these embodiments the ballast would be primarily located as part of the other groups. Furthermore, even if the coupling-off group Z contains a ballast it is often necessary to ballast the other substituents as well, since Z is eliminated from the molecule upon coupling; thus, the ballast is most advantageously provided as part of groups other than Z.
The following examples further illustrate preferred coupler of the invention. It is not to be construed that the present invention is limited to these examples. 
Preferred couplers are IC-3, IC-7, IC-35, and IC-36 because of their suitably narrow left bandwidths.
Couplers that form magenta dyes upon reaction with oxidized color developing agent are described in such representative patents and publications as: U.S. Pat. Nos. 2,311,082; 2,343,703; 2,369,489; 2,600,788; 2,908,573; 3,062,653; 3,152,896; 3,519,429; 3,758,309; and xe2x80x9cFarbkuppler-eine Literature Ubersicht,xe2x80x9d published in Agfa Mitteilungen, Band III, pp. 126-156 (1961). Preferably such couplers are pyrazolones, pyrazolotriazoles, or pyrazolobenzirnidazoles that form magenta dyes upon reaction with oxidized color developing agents. Especially preferred couplers are 1H-pyrazolo [5,1-c]-1,2,4-triazole and 1H-pyrazolo [1,5-b]-1,2,4-triazole. Examples of 1H-pyrazolo [5,1-c]-1,2,4-triazole couplers are described in U.K. Patent Nos. 1,247,493; 1,252,418; 1,398,979; U.S. Pat. Nos. 4,443,536; 4,514,490; 4,540,654; 4,590,153; 4,665,015; 4,822,730; 4,945,034; 5,017,465; and 5,023,170. Examples of 1H-pyrazolo [1,5-b]-1,2,4-triazoles can be found in European Patent applications 176,804; 177,765; U.S Pat. Nos. 4,659,652; 5,066,575; and 5,250,400.
Typical pyrazoloazole and pyrazolone couplers are represented by the following formulas: 
wherein Ra and Rb independently represent H or a substituent; Rc is a substituent (preferably an aryl group); Rd is a substituent (preferably an anilino, carbonamido, ureido, carbamoyl, alkoxy, aryloxycarbonyl, alkoxycarbonyl, or N-heterocyclic group); X is hydrogen or a coupling-off group; and Za, Zb, and Zc are independently a substituted methine group, xe2x95x90Nxe2x80x94, xe2x95x90Cxe2x80x94, or xe2x80x94NHxe2x80x94, provided that one of either the Zaxe2x80x94Zb bond or the Zbxe2x80x94Zc bond is a double bond and the other is a single bond, and when the Zbxe2x80x94Zc bond is a carbonxe2x80x94carbon double bond, it may form part of an aromatic ring, and at least one of Za, Zb, and Zc represents a methine group connected to the group Rb.
Specific examples of such couplers are: 
Couplers that form yellow dyes upon reaction with oxidized color developing agent are described in such representative patents and publications as: U.S. Pat. Nos. 2,298,443; 2,407,210; 2,875,057; 3,048,194; 3,265,506; 3,447,928; 3,960,570; 4,022,620; 4,443,536; 4,910,126; and 5,340,703 and xe2x80x9cFarbkuppler-eine Literature Ubersicht,xe2x80x9d published in Agfa Mitteilungen, Band III, pp. 112-126 (1961). Such couplers are typically open chain ketomethylene compounds. Also preferred are yellow couplers such as described in, for example, European Patent Application Nos. 482,552; 510,535; 524,540; 543,367; and U.S. Pat. No. 5,238,803. For improved color reproduction, couplers which give yellow dyes that cut off sharply on the long wavelength side are particularly preferred (for example, see U.S. Pat. No. 5,360,713).
Typical preferred yellow couplers are represented by the following formulas: 
wherein R1, R2, Q1 and Q2 each represents a substituent; X is hydrogen or a coupling-off group; Y represents an aryl group or a heterocyclic group; Q3 represents an organic residue required to form a nitrogen-containing heterocyclic group together with the  greater than Nxe2x80x94; and Q4 represents nonmetallic atoms necessary to from a 3- to 5-membered hydrocarbon ring or a 3- to 5-membered heterocyclic ring which contains at least one hetero atom selected from N, O, S, and P in the ring. Particularly preferred is when Q1 and Q2 each represents an alkyl group, an aryl group, or a heterocyclic group, and R2 represents an aryl or tertiary alkyl group.
Preferred yellow couplers can be of the following general structures: 
Unless otherwise specifically stated, substituent groups which may be substituted on molecules herein include any groups, whether substituted or unsubstituted, which do not destroy properties necessary for photographic utility. When the term xe2x80x9cgroupxe2x80x9d is applied to the identification of a substituent containing a substitutable hydrogen, it is intended to encompass not only the substituent""s unsubstituted form, but also its form further substituted with any group or groups as herein mentioned. Suitably, the group may be halogen or may be bonded to the remainder of the molecule by an atom of carbon, silicon, oxygen, nitrogen, phosphorous, or sulfur. The substituent may be, for example, halogen, such as chlorine, bromine or fluorine; nitro; hydroxyl; cyano; carboxyl; or groups which may be further substituted, such as alkyl, including straight or branched chain alkyl, such as methyl, trifluoromethyl, ethyl, 1-butyl, 3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such as ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy; aryl such as phenyl, 4-t-butylphenyl, 2,4,6-trimethylphenyl, naphthyl; aryloxy, such as phenoxy, 2-methylphenoxy, alpha- or betanaphthyloxy, and 4-tolyloxy; carbonamido, such as acetamido, benzamido, butyramido, tetradecanamido, alpha-(2,4-di-t-pentyl-phenoxy)acetarnido, alpha-(2,4-di-t-pentylphenoxy)butyramido, alpha-(3-pentadecylphenoxy)-hexanamido, alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido, 2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-1-yl, N-methyltetradecanamido, N-succinimido, N-phthalimido, 2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo- 1-imidazolyl, and N-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino, benzyloxycarbonylamino, hexadecyloxycarbonylamino, 2,4-di-t-butylphenoxycarbonylamino, phenylcarbonylamino, 2,5-(di-t-pentylphenyl)carbonylamino, p-dodecyl-phenylcarbonylamino, p-toluylcarbonylamino, N-methylureido, N,N-dimethylureido, N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido, N,N-dioctyl-Nxe2x80x2-ethylureido, N-phenylureido, N,N-diphenylureido, N-phenyl-N-p-toluylureido, N-(m-hexadecylphenyl)ureido, N,N-(2,5-di-t-pentylphenyl)-Nxe2x80x2-ethylureido, and t-butylcarbonamido; sulfonamido, such as methylsulfonamido, benzenesulfonamido, p-toluylsulfonamido, p-dodecylbenzenesulfonamido, N-methyltetradecylsulfonamido, N,N-dipropyl-sulfamoylamino, and hexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl, N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl, N,N-dimethylsulfamoyl; N-[3-(dodecyloxy)propyl]sulfamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl, N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl, such as N-methylcarbamoyl, N,N-dibutylcarbamoyl, N-octadecylcarbamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl, N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl, such as acetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl, p-dodecyloxyphenoxycarbonyl, methoxycarbonyl, butoxycarbonyl, tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl, 3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such as methoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl, 2-ethylhexyloxysulfonyl, phenoxysulfonyl, 2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl, 2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl, phenylsulfonyl, 4-nonylphenylsulfonyl, and p-toluylsulfonyl; sulfonyloxy, such as dodecylsulfonyloxy, and hexadecylsulfonyloxy; sulfinyl, such as methylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl, hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl, and p-toluylsulfinyl; thio, such as ethylthio, octylthio, benzylthio, tetradecylthio, 2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio, 2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such as acetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy, N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and cyclohexylcarbonyloxy; amino, such as phenylanilino, 2-chloroanilino, diethylamino, dodecylamino; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or 3-benzylhydantoinyl; phosphate, such as dimethylphosphate and ethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; a heterocyclic group, a heterocyclic oxy group or a heterocyclic thio group, each of which may be substituted and which contain a 3 to 7 membered heterocyclic ring composed of carbon atoms and at least one hetero atom selected from the group consisting of oxygen, nitrogen and sulfur, such as 2-furyl, 2-thienyl, 2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such as triethylarnmonium; and silyloxy, such as trimethylsilyloxy.
If desired, the substituents may themselves be further substituted one or more times with the described substituent groups. The particular substituents used may be selected by those skilled in the art to attain the desired photographic properties for a specific application and can include, for example, hydrophobic groups, solubilizing groups, blocking groups, releasing or releasable groups, etc. Generally, the above groups and substituents thereof may include those having up to 48 carbon atoms, typically 1 to 36 carbon atoms and usually less than 24 carbon atoms, but greater numbers are possible depending on the particular substituents selected.
Representative substituents on ballast groups include alkyl, aryl, alkoxy, aryloxy, alkylthio, hydroxy, halogen, alkoxycarbonyl, aryloxcarbonyl, carboxy, acyl, acyloxy, amino, anilino, carbonamido, carbamoyl, alkylsulfonyl, arylsulfonyl, sulfonamido, and sulfamoyl groups wherein the substituents typically contain 1 to 42 carbon atoms. Such substituents can also be further substituted.
Stabilizers and scavengers that can be used in these photographic elements, but are not limited to, the following. 
Examples of solvents which may be used in the invention include the following:
The dispersions used in photographic elements may also include ultraviolet (UV) stabilizers and so called liquid UV stabilizers such as described in U.S. Pat. Nos. 4,992,358; 4,975,360; and 4,587,346. Examples of UV stabilizers are shown below. 
The aqueous phase may include surfactants. Surfactant may be cationic, anionic, zwitterionic or non-ionic. Useful surfactants include, but are not limited to, the following: 
Further, it is contemplated to stabilize photographic dispersions prone to particle growth through the use of hydrophobic, photographically inert compounds such as disclosed by Zengerle et al in U.S. Pat. No. 5,468,604.
In a preferred embodiment the invention employs recording elements which are constructed to contain at least three silver halide emulsion layer units. A suitable full color, multilayer format for a recording element used in the invention is represented by Structure I.
wherein the red-sensitized, cyan dye image-forming silver halide emulsion unit is situated nearest the support; next in order is the green-sensitized, magenta dye image-forming unit, followed by the uppermost blue-sensitized, yellow dye image-forming unit. The image-forming units are separated from each other by hydrophilic colloid interlayers containing an oxidized developing agent scavenger to prevent color contamination. Silver halide emulsions satisfying the grain and gelatino-peptizer requirements described above can be present in any one or combination of the emulsion layer units. Additional useful multicolor, multilayer formats for an element of the invention include structures as described in U.S. Pat. No. 5,783,373. Each of such structures in accordance with the invention preferably would contain at least three silver halide emulsions comprised of high chloride grains having at least 50 percent of their surface area bounded by {100} crystal faces and containing dopants from classes (i) and (ii), as described above. Preferably each of the emulsion layer units contains emulsion satisfying these criteria.
Conventional features that can be incorporated into multilayer (and particularly multicolor) recording elements contemplated for use in the method of the invention are illustrated by Research Disclosure, Item 38957, cited above:
XI. Layers and layer arrangements
XII. Features applicable only to color negative
XIII. Features applicable only to color positive
B. Color reversal
C. Color positives derived from color negatives
XIV. Scan facilitating features.
The recording elements comprising the radiation sensitive high chloride emulsion layers according to this invention can be conventionally optically printed, or in accordance with a particular embodiment of the invention can be image-wise exposed in a pixel-by-pixel mode using suitable high energy radiation sources typically employed in electronic printing methods. Suitable actinic forms of energy encompass the ultraviolet, visible and infrared regions of the electromagnetic spectrum as well as electron-beam radiation and is conveniently supplied by beams from one or more light emitting diodes or lasers, including gaseous or solid state lasers. Exposures can be monochromatic, orthochromatic or panchromatic. For example, when the recording element is a multilayer multicolor element, exposure can be provided by laser or light emitting diode beams of appropriate spectral radiation, for example, infrared, red, green or blue wavelengths, to which such element is sensitive. Multicolor elements can be employed which produce cyan, magenta and yellow dyes as a function of exposure in separate portions of the electromagnetic spectrum, including at least two portions of the infrared region, as disclosed in the previously mentioned U.S. Pat. No. 4,619,892. Suitable exposures include those up to 2000 nm, preferably up to 1500 nm. Suitable light emitting diodes and commercially available laser sources are known and commercially available. Imagewise exposures at ambient, elevated or reduced temperatures and/or pressures can be employed within the useful response range of the recording element determined by conventional sensitometric techniques, as illustrated by T. H. James, The Theory of the Photographic Process, 4th Ed., Macmillan, 1977, Chapters 4, 6, 17, 18 and 23.
It has been observed that anionic [MXxYyLz] hexacoordination complexes, where M is a group 8 or 9 metal (preferably iron, ruthenium or iridium), X is halide or pseudohalide (preferably Cl, Br or CN) x is 3 to 5, Y is H2O, y is 0 or 1, L is a Cxe2x80x94C, Hxe2x80x94C or Cxe2x80x94Nxe2x80x94H organic ligand, and Z is 1 or 2, are surprisingly effective in reducing high intensity reciprocity failure (HIRF), low intensity reciprocity failure (LIRF) and thermal sensitivity variance and in in improving latent image keeping (LIK). As herein employed HIRF is a measure of the variance of photographic properties for equal exposures, but with exposure times ranging from 10xe2x88x921 to 10xe2x88x926 second. LIRF is a measure of the varinance of photographic properties for equal exposures, but with exposure times ranging from 10xe2x88x921 to 100 seconds. Although these advantages can be generally compatible with face centered cubic lattice grain structures, the most striking improvements have been observed in high ( greater than 50 mole %, preferably  greater than 90 mole %) chloride emulsions. Preferred Cxe2x80x94C, Hxe2x80x94C or Cxe2x80x94Nxe2x80x94H organic ligands are aromatic heterocycles of the type described in U.S. Pat. No. 5,462,849. The most effective Cxe2x80x94C, Hxe2x80x94C or Cxe2x80x94Nxe2x80x94H organic ligands are azoles and azines, either unsustituted or containing alkyl, alkoxy or halide substituents, where the alkyl moieties contain from 1 to 8 carbon atoms. Particularly preferred azoles and azines include thiazoles, thiazolines and pyrazines.
The quantity or level of high energy actinic radiation provided to the recording medium by the exposure source is generally at least 10xe2x88x924 ergs/cm2, typically in the range of about 10xe2x88x924 ergs/cm2 to 10xe2x88x923 ergs/cm2 and often from 10xe2x88x923 ergs/cm2 to 102 ergs/cm2. Exposure of the recording element in a pixel-by-pixel mode as known in the prior art persists for only a very short duration or time. Typical maximum exposure times are up to 100xcexc seconds, often up to 10xcexc seconds, and frequently up to only 0.5xcexc seconds. Single or multiple exposures of each pixel are contemplated. The pixel density is subject to wide variation, as is obvious to those skilled in the art. The higher the pixel density, the sharper the images can be, but at the expense of equipment complexity. In general, pixel densities used in conventional electronic printing methods of the type described herein do not exceed 107 pixels/cm2 and are typically in the range of about 104 to 106 pixels/cm2. An assessment of the technology of high-quality, continuous-tone, color electronic printing using silver halide photographic paper which discusses various features and components of the system, including exposure source, exposure time, exposure level and pixel density and other recording element characteristics is provided in Firth et al., A Continuous-Tone Laser Color Printer, Journal of Imaging Technology, Vol. 14, No. 3, June 1988, which is hereby incorporated herein by reference. As previously indicated herein, a description of some of the details of conventional electronic printing methods comprising scanning a recording element with high energy beams such as light emitting diodes or laser beams, are set forth in Hioki U.S. Pat. No. 5,126,235, European Patent Applications 479 167 A1 and 502 508 A1.
Once imagewise exposed, the recording elements can be processed in any convenient conventional manner to obtain a viewable image. Such processing is illustrated by Research Disclosure, Item 38957, cited above:
XVIII. Chemical development systems
XIX. Development
XX. Desilvering, washing, rinsing and stabilizing
In addition, a usefull developer for the inventive material is a homogeneous, single part developing agent. The homogeneous, single-part color developing concentrate is prepared using a critical sequence of steps:
In the first step, an aqueous solution of a suitable color developing agent is prepared. This color developing agent is generally in the form of a sulfate salt. Other components of the solution can include an antioxidant for the color developing agent, a suitable number of alkali metal ions (in an at least stoichiometric proportion to the sulfate ions) provided by an alkali metal base, and a photographically inactive water-miscible or water-soluble hydroxy-containing organic solvent. This solvent is present in the final concentrate at a concentration such that the weight ratio of water to the organic solvent is from about 15:85 to about 50:50.
In this environment, especially at high alkalinity, alkali metal ions and sulfate ions form a sulfate salt that is precipitated in the presence of the hydroxy-containing organic solvent. The precipitated sulfate salt can then be readily removed using any suitable liquid/solid phase separation technique (including filtration, centrifugation or decantation). If the antioxidant is a liquid organic compound, two phases may be formed and the precipitate may be removed by discarding the aqueous phase.
The color developing concentrates of this invention include one or more color developing agents that are well known in the art that, in oxidized form, will react with dye forming color couplers in the processed materials. Such color developing agents include, but are not limited to, aminophenols, p-phenylenediamines (especially N,N-dialkyl-p-phenylenediamines) and others which are well known in the art, such as EP 0 434 097 A1 (published Jun. 26, 1991) and EP 0 530 921 A1 (published Mar. 10, 1993). It may be useful for the color developing agents to have one or more water-solubilizing groups as are known in the art. Further details of such materials are provided in Research Disclosure, publication 38957, pages 592-639 (September 1996). Research Disclosure is a publication of Kenneth Mason Publications Ltd., Dudley House, 12 North Street, Emsworth, Hampshire PO10 7DQ England (also available from Emsworth Design Inc., 121 West 19th Street, New York, N.Y. 10011). This reference will be referred to hereinafter as xe2x80x9cResearch Disclosurexe2x80x9d. 
Preferred color developing agents include, but are not limited to, N,N-diethyl p-phenylenediamine sulfate (KODAK Color Developing Agent CD-2), 4-amino-3-methyl-N-(2-methane sulfonamidoethyl)aniline sulfate, 4-(N-ethyl-N-p-hydroxyethylamino)-2-methylaniline sulfate (KODAK Color Developing Agent CD4), p-hydroxyethylethylaminoaniline sulfate, 4-(N-ethyl-N-2-methanesulfonylaminoethyl)-2-methylphenylenediamine sesquisulfate (KODAK Color Developing Agent CD-3), 4-(N-ethyl-N-2-methanesulfonylaminoethyl)-2-methylphenylenediamine sesquisulfate, and others readily apparent to one skilled in the art.
In order to protect the color developing agents from oxidation, one or more antioxidants are generally included in the color developing compositions. Either inorganic or organic antioxidants can be used. Many classes of useful antioxidants are known, including but not limited to, sulfites (such as sodium sulfite, potassium sulfite, sodium bisulfite and potassium metabisulfite), hydroxylamine (and derivatives thereof), hydrazines, hydrazides, amino acids, ascorbic acid (and derivatives thereof), hydroxamic acids, aminoketones, mono- and polysaccharides, mono- and polyamines, quaternary ammonium salts, nitroxy radicals, alcohols, and oximes. Also useful as antioxidants are 1,4-cyclohexadiones. Mixtures of compounds from the same or different classes of antioxidants can also be used if desired.
Especially usefull antioxidants are hydroxylamine derivatives as described, for example, in U.S. Pat. Nos. 4,892,804; 4,876,174; 5,354,646; and 5,660,974, all noted above, and U.S. Pat. No. 5,646,327 (Burns et al). Many of these antioxidants are mono- and dialkylhydroxylamines having one or more substituents on one or both alkyl groups. Particularly useful alkyl substituents include sulfo, carboxy, amino, sulfonamido, carbonamido, hydroxy, and other solubilizing substituents.
More preferably, the noted hydroxylamine derivatives can be mono- or dialkylhydroxylamines having one or more hydroxy substituents on the one or more alkyl groups. Representative compounds of this type are described for example in U.S. Pat. No. 5,709,982 (Marrese et al), as having the structure I: 
wherein R is hydrogen, a substituted or unsubstituted alkyl group of 1 to 10 carbon atoms, a substituted or unsubstituted hydroxyalkyl group of 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group of 5 to 10 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms in the aromatic nucleus.
X1 is xe2x80x94CR2(OH)CHR1xe2x80x94 and X2 is xe2x80x94CHR1CR2(OH)xe2x80x94 wherein R1 and R2 are independently hydrogen, hydroxy, a substituted or unsubstituted alkyl group or 1 or 2 carbon atoms, a substituted or unsubstituted hydroxyalkyl group of 1 or 2 carbon atoms, or R1 and R2 together represent the carbon atoms necessary to complete a substituted or unsubstituted 5- to 8-membered saturated or unsaturated carbocyclic ring structure.
Y is a substituted or unsubstituted alkylene group having at least 4 carbon atoms, and has an even number of carbon atoms, or Y is a substituted or unsubstituted divalent aliphatic group having an even total number of carbon and oxygen atoms in the chain, provided that the aliphatic group has a least 4 atoms in the chain.
Also in Structure I, m, n and p are independently 0 or 1. Preferably, each of m and n is 1, and p is 0.
Specific di-substituted hydroxylamine antioxidants include, but are not limited to, N,N-bis(2,3-dihydroxypropyl)hydroxylamine, N,N-bis(2-methyl-2,3-dihydroxypropyl)hydroxylamine and N,N-bis(1-hydroxymethyl-2-hydroxy-3-phenylpropyl)hydroxylamine. The first compound is preferred.